As disclosed in JP 2003-214516 (A), JP 2007-315595 (A), JP 2008-025821 (A) and JP 2008-275088 (A) and the like, the use of a half-toroidal continuously-variable transmission as an automobile transmission is well known. Moreover, JP 2004-169719 (A) discloses construction that increases the adjustable range of the transmission ratio by combining a toroidal continuously-variable transmission and a planetary-gear mechanism.
FIG. 21 and FIG. 22 illustrate a first example of conventional construction of a toroidal continuously-variable transmission. In this first example of conventional construction, a pair of input disks 2 are supported around portions near both ends of an input rotating shaft 1 so that the inside surfaces thereof, which are toroidal curved surfaces, face each other, and so as to be able to rotate in synchronization with the input rotating shaft 1. Moreover, an output cylinder 3 is supported around the middle section of the input rotating shaft 1 so as to be able to rotate with respect to the input rotating shaft 1. An output gear 4 is fastened to the center section in the axial direction of the outer-circumferential surface of the output cylinder 3, and a pair of output disks 5 is supported around the both end sections in the axial direction of the outer-circumferential surface of the output cylinder 3 by spline engagement so as to be able to rotate synchronously with the output cylinder 3. In this state, the inside surfaces, which are toroidal curved surfaces, of the pair of output disks 5 are made to face the inside surfaces of the input disks 2.
Moreover, plural power rollers 6, the peripheral surfaces of which are spherical convex surfaces, are held between the input disks 2 and output disks 5. The power rollers 6 are supported by trunnions 7 so as to freely rotate, and the trunnions 7 are supported so as to pivotally rotate around pivot shafts 8 that are located in skewed positions with respect to the center axis of the input disks 2 and output disks 5. In other words, each trunnion 7 comprises a pair of pivot shafts 8 that are provided on both end sections in the axial direction thereof so as to be concentric with each other, and a support beam 9 that exists between the pivot shafts 8; and the pivot shafts 8 are supported by a support plate 10 by way of a radial needle bearing 11.
Moreover, each power roller 6 is supported by the inside surface of the support beam 9 of the trunnion 7 by way of a support shaft 12, of which the base-end half section and tip-end half section are eccentric with each other, and plural rolling bearings so as to be able to rotate around the tip-end half section of the support shaft 12 and so as to be able to pivotally displace a little around the base-end half section of the support shaft 12. In other words, a thrust ball bearing 13 and a thrust needle bearing 14 are provided in that order from the power roller side between the outside surface of the power roller 6 and the inside surface of the support beam 9 of the trunnion 7. The thrust ball bearing 13 is for supporting loads in the thrust direction that are applied to the power roller 6, and for allowing rotation of the power roller 6 around the tip-end half section of the support shaft 12. The thrust ball bearing 13 is constructed by providing plural balls 18 between an inner-ring raceway 15 that is formed around the outside surface of the power roller 6 and an outer-ring raceway 17 that is formed around the inside surface of an outer ring 16 so as to be able to roll. Moreover, the thrust needle bearing 14 is for supporting thrust loads that are applied from the power roller 6 to the outer ring 16 of the thrust ball bearing 13, and for allowing the outer ring 16 and the tip-end half section of the support shaft 12 to pivot around the base-end half section of the support shaft 12.
During operation of this kind of toroidal continuously-variable transmission, a drive shaft 19 rotates and drives one input disk 2 (left input disk 2 in FIG. 21) by way of a pressure apparatus 20. As a result, the pair of input disks 2 that are supported on both ends of the input rotating shaft 1 are rotated in synchronization while being pressed in a direction toward each other. The rotation of the pair of input disks 2 is transmitted to the pair of output disks 5 by way of the power rollers 6, and outputted from the output gear 4. When changing the transmission ratio between the input rotating shaft 1 and the output gear 4, hydraulic actuators 21 cause the trunnions 7 to displace in the axial direction of the pivot shafts 8. As a result, the directions of forces in the tangential direction that act at the areas of rolling contact (traction sections) between the peripheral surfaces of the power rollers 6 and the inside surfaces of the input disks 2 and output disks 5 changes, or in other words, side slipping occurs at the areas of rolling contact. As the directions of forces in the tangential direction change in this way, the trunnions 7 pivot around the pivot shafts 8, and the positions of contact between the peripheral surfaces of the power rollers 6 and the inside surfaces of the input disks 2 change. By bringing the peripheral surfaces of the power rollers 6 in rolling contact with the portions on the outside in the radial direction of the inside surfaces of the input disks 2, and with the portions near the inside in the radial direction of the inside surfaces of the output disk 5, the transmission ratio between the input rotating shaft 1 and the output gear 4 is on the accelerating side. On the other hand, by bringing the peripheral surfaces of the power rollers 6 in rolling contact with the portions on the inside in the radial direction of the inside surfaces of the input disks 2, and with the portions near the outside in the radial direction of the inside surfaces of the output disks 5, the transmission ratio between the input rotating shaft 1 and the output gear 4 is on the decelerating side.
During operation of a toroidal continuously-variable transmission such as described above, all of the members that contribute to the transmission of power, or in other words, the input disks 2, output disks 5 and power rollers 6 elastically deform due to the pressure force generated by the pressure apparatus 20. Then, as these members elastically deform, the input disks 2 and output disks 5 displace in the axial direction. Moreover, the pressure force that is generated by the pressure apparatus 20 becomes larger the larger the torque is that is transmitted by the toroidal continuously-variable transmission, and as the pressure force becomes larger, the amount of elastic deformation of these members 2, 5, 6 also increases. Therefore, in order to properly maintain a state of contact between the inside surfaces of the input disks 2 and output disks 5 and the peripheral surfaces of the power rollers 6 regardless of change in the torque that is transmitted by the toroidal continuously-variable transmission, a mechanism that causes the power rollers 6 to displace with respect to the trunnions 7 in the axial direction of the input disks 2 and output disks 5 becomes necessary.
In the case of the first example of conventional construction, the power rollers 6 are caused to displace in the axial direction of the input disks 2 and output disks 5 by causing the tip-end half section of the support shafts 12 that support the power rollers 6 to pivotally displace around the base-end half section of the support shafts 12. However, the construction for causing the power rollers 6 to displace in the axial direction of the input disks 2 and output disks 5 becomes complex, so production and management of parts, and the assembly work all become troublesome and an increase in cost cannot be avoided.
On the other hand, JP 20030214516 (A) discloses construction such as illustrated in FIG. 23 to FIG. 28. A feature of this second example of conventional construction is the portion for supporting the power rollers 6a by the trunnions 7a so as to be able to displace in the axial direction of the input disks 2 and output disks 5 (see FIG. 21). The trunnions 7a of this second example of conventional construction comprise a pair of pivot shafts 8a, 8b that are provided on both ends so as to be concentric with each other, and a support beam section 23 that is located between the pivot shafts 8a, 8b, with at least the side surface on the inside (top side in FIG. 24, FIG. 27 and FIG. 28) in the radial direction (up-down direction in FIG. 24, FIG. 27 and FIG. 28) of the input disks 2 and output disks 5 (see FIG. 21) being a cylindrical convex surface 22. The pivot shafts 8a, 8b are supported by a support plate 10 (see FIG. 22) by way of a radial needle bearing 11a so as to be able to pivot and to displace in the axial direction.
As illustrated in FIG. 24 and FIG. 27, the center axis α of the cylindrical convex surface 22 is parallel to the center axis β of the pivot shafts 8a, 8b and is located further on the outside (bottom side in FIG. 24, FIG. 27 and FIG. 28) in the radial direction of the input disks 2 and output disks 5. Moreover, a partial cylindrical surface shaped concave section 24 is provided on the outside surface of the outer ring 16a of a thrust ball bearing 13a that is provided between the support beam section 23 and the outside surface of the power roller 6a so as to cross the outside surface of the outer ring 16a in the radial direction. By fitting the concave section 24 with the cylindrical convex surface 22 of the support beam section 23, the outer ring 16a is supported by the trunnion 7a so as to be able to pivotally displace in the axial direction of the input disk 2 and output disk 5.
A support shaft 12a is fixed to the center section of the inside surface of the outer ring 16a so as to be integrally provided with the outer ring 16a, and the power roller 6a is supported around the support shaft 12a by way of a radial needle bearing 25 so as to rotate freely. Furthermore, a pair of stepped surfaces 26 that face each other are provided in the connecting section between both ends of the support beam 23 and the pair of pivot shafts 8a, 8b of the inside surface of the trunnion 7a. By having the pair of stepped surfaces 29 come in contact with or closely facing the outer-circumferential surface of the outer ring 16a of the thrust ball bearing 13, the traction force that is applied from the power roller 6a to the outer ring 16a can be supported by one of the stepped surfaces 26.
This second example of conventional construction causes the power rollers 6a to displace in the axial direction of the input disks 2 and output disks 5, and regardless of change in the amount of elastic deformation of these members 2, 5, 6a, construction that properly maintains the state of contact between the peripheral surfaces of the power rollers 6a and the inside surfaces of the input disks 2 and output disks 5 is achieved simply and at low cost.
In other words, during operation of the toroidal continuously-variable transmission, when it is necessary to cause the power rollers 6a to displace in the axial direction of the input disks 2 and output disks 5 due to elastic deformation of the members 2, 5, 6a, the outer rings 16a of the thrust ball bearings 13a that support the power rollers 6a so as to freely rotate, pivotally displace around the center axes a of the cylindrical convex surfaces 22 while there is sliding of contact surfaces between the concave sections 24 of the outer ring 16a and the cylindrical convex surfaces 22 of the support beams 23. Due to the pivotal displacement of the outer rings 16a, the portions of the peripheral surfaces of the power rollers 6a that come in rolling contact with one of the side surfaces in the axial direction of the input disks 2 and output disks 5 displace in the axial direction of these disks 2, 5, and the state of contact between the peripheral surfaces of the power rollers 6a and the inside surfaces of these disks 2, 5 is properly maintained.
The center axis α of the cylindrical convex surface 22 is located further on the outside in the radial direction of the input disk 2 and output disk 5 than the center axis β of the pivot shafts 8a, 8b, which is the pivot center of the trunnion 7a during a speed change operation. Therefore, the radius of pivotal displacement around the center axis α of the cylindrical convex surface 22 is greater than the pivot radius during a speed change operation, so there is little effect on fluctuation of the transmission ratio between the input disk 2 and output disk 5, which can be ignored or remains within a range that can be easily corrected.
However, in this second example of conventional construction as well, from the aspect of stabilizing a speed change operation, there is room for improvement. In other words, in order to smoothly perform the pivotal displacement of the outer ring 16a around the support beam 23, the space “D” between the pair of stepped surfaces 26 that are provided on both ends of the support beam 23 must be made a little larger than the outer diameter “d” of the outer ring 16a (D>d). Therefore, the outer ring 16a and the power roller 6a that is supported concentric with the outer ring 16a are able to displace in the axial direction of the support beam 23 by the amount of the difference between the space “D” between the stepped surfaces 26 and the outer diameter “d” of the outer ring 16a (D−d).
On the other hand, during operation of a vehicle in which a toroidal continuously-variable transmission is installed, a force called “2Ft” that is well known in the technical field of toroidal continuously-variable transmissions is applied to the power rollers 6a from the input disks 2 and output disks 5 in opposite directions between at acceleration and at deceleration (during engine braking). Due to this force “2Ft”, the power rollers 6a displace in the axial direction of the support beams 23 together with the outer rings 16a. The direction of displacement of the support beams 23 is the same as the direction of displacement of the trunnions 7 (see FIG. 22) due to actuators 21, and even when the amount of displacement is about 0.1 mm, there is a possibility that a speed change operation will start. When a speed change operation starts due to such a cause, the speed change operation is not directly related to the operation of the vehicle, and even when correction is performed, a feeling that something is wrong is given to the driver. Particularly, when a speed change that is not intended by the driver is performed in a state in which the torque transmitted by the toroidal continuously-variable transmission is low, it is easy for the feeling given to the driver that something is wrong to become large.
In order to suppress the generation of speed change operations such as this that are not directly related to the vehicle operation, it is possible to make the difference between the distance “D” between the pair of stepped surfaces 26 and the outer diameter “d” of the outer ring 16a (D−d) minimized, for example, tens of μm. However, during operation of a half-toroidal type of toroidal continuously-variable transmission, due to the thrust load that is applied from the traction area to the support beam 23 by way of the power roller 6a and outer ring 16a, the trunnion 7a, as exaggeratedly illustrated in FIG. 29, elastically deforms in a direction such that the side where the outer ring 16a is located becomes concave. As a result of this elastic deformation, the space between the pair of stepped surfaces 26 that are provided for each trunnion 7a is reduced. In such a state as well, in order that the space “D” between the pair of stepped surfaces 26 does not become equal to or less than the outer diameter “d” of the outer ring 16a, it is necessary to maintain a certain amount of difference between the space “D” and outer diameter “d” when the trunnion 7a is in the normal state with no elastic deformation. As a result, during operation at low torque when it is particularly easy for a feeling that something is wrong to occur, it becomes easy for a speed change operation that is not directly related to the vehicle operation to occur. Especially, as disclosed in JP 2004-169719 (A), in the case of a continuously-variable transmission that is a combination of a toroidal continuously-variable transmission, a planetary-gear transmission, and clutch apparatus, and that switches between a low-speed mode and high-speed mode by way of the clutch apparatus, as the mode is switched while remaining in the acceleration state, the direction of the torque that passes through the toroidal continuously-variable transmission is reversed. Therefore, a speed change operation such as described above that is not directly related to the vehicle operation occurs, and that operation gives the driver a feeling that something is wrong.
JP 2008-025821 (A) discloses construction for supporting the force “2Ft” by fitting an anchor piece that is fastened to part of a cylindrical convex surface that is provided on a support beam side together with an anchor groove that is formed in the inside surface of a concave section on an outer ring side. With this construction, fastening the anchor piece to the support beam and supporting the anchor piece so as to be able to maintain the strength and rigidity to be able to support the force “2Ft” is difficult, as well as it becomes difficult to lower cost and maintain sufficient reliability. Moreover, construction is also disclosed in which the force “2Ft” is supported by plural balls that are located between rolling grooves having arc shaped cross sections that are formed in the portions of a cylindrical convex surface and a concave section that are aligned with each other. In this construction, as the force “2Ft” becomes larger and the surface pressure at the areas of rolling contact between the rolling surfaces of the balls and the rolling grooves increases, there is a possibility that indentations will be formed in the inner surfaces of the rolling grooves, and that vibration will occur when the inner ring pivotally displaces with respect to the trunnion. Furthermore, construction is also disclosed in which the force “2Ft” is supported by fitting together a protrusion that is formed around the outer-circumferential surface of the support beam such that surfaces on both sides in the axial direction thereof are parallel to each other, with a concave groove that is formed around the inside surface of a concave section on the outer-ring side. In this construction, during polishing in order to precisely finish the space between the side surfaces of the protrusion in order to reduce gaps in the section where the protrusion fits with the concave groove, it is easy for damage to occur on the side surfaces due to polishing burn. In other words, the polishing process is performed by pressing a rotating grindstone against the side surfaces of the protrusion. When doing this, the side surfaces of the protrusion, which are the surfaces to be processed, are parallel to each other, or in other words, these side surfaces are perpendicular to the axis of rotation of the grindstone, so it is easy polishing burn to occur due to an increase in temperature of these side surfaces. Moreover, the axial direction of the axis of rotation of the grindstone and the direction the grindstone is pressed are parallel, so it is not possible to polish the side surfaces of the protrusion and the cylindrical convex surface at the same time, so the processing efficiency is bad, and the manufacturing cost of the overall trunnion increases.